The present invention generally relates to adsorbents for oxygen, water and carbon dioxide and, more specifically, to an improved adsorbent for the cryogenic storage of oxygen and the simultaneous release of oxygen with removal of carbon dioxide and water from the environment and the release of heat.
Present and future space and underwater explorations require advanced life support systems that are more integrated and have higher volumetric and gravimetric efficiencies. Two essential elements of an advanced life support system are the supply of oxygen and the removal of contaminants, such as carbon dioxide, water, and other potentially harmful trace materials.
Oxygen is an essential gas for the maintenance of human life, especially in space exploration, underwater activities, and underground activities, such as mining. The ability to store and later release oxygen as required to support processes is an important technology.
Carbon dioxide and water are produced from biological processes, combustion of fossil fuels, and from other industrial processes. For the maintenance of human lifexe2x80x94especially in space exploration, underwater activities, and underground mining activitiesxe2x80x94the control of the concentration of carbon dioxide and water are critically important. In addition, carbon dioxide has been identified as one of the global warming gases. There are other trace contaminants, such as NOx, SOx, and H2S, that are removed along with the carbon dioxide and water.
Zeolite materials such as 13X, 4A, and 5A are commonly used adsorbents for storing oxygen and removal of carbon dioxide. These adsorbent materials are inorganic oxides that also adsorb water. These zeolites exhibit a low oxygen capacity of about 30% (weight/weight) at cryogenic temperatures.
Conventional methods of oxygen generation used for respiratory support systems in underwater activities, such as submarines, in space activities, in underground activities and in aircraft activities are based primarily on chlorates, perchlorates, peroxides, and superoxides. The chlorates and perchlorates of lithium, sodium, and potassium evolve oxygen when heated. When these salts are compounded with a fuel, a chlorate-based candle is formed that produces oxygen continuously by thermal decomposition. Large candles capable of delivering 3-4 m3 oxygen in 45 minutes have been used in submarines for long submergence operations. Chlorate candles have also been used in the Apollo moon mission.
In an effort to overcome disadvantages presented by chlorate-based candles and similar systems for the generation of oxygen, carbon-based materials have been used. For example, in U.S. Pat. No. 4,820,681 which is assigned to the assignee of the present invention, a carbon molecular sieve was prepared by polymerizing a cross-linking agent and a precursor monomer to produce a cross-linked polymer. The cross-linked polymer was then shaped into a desired configuration without the need for a binder. The shaped polymer was then carbonized.
In a fashion related to the above patent, U.S. Pat. No. 4,810,266 which is also assigned to the assignee of the present invention discloses a carbon molecular sieve. The sieve is similarly prepared by polymerizing a cross-linking agent and precursor monomer. The cross-linked polymer that is produced was also shaped into a desired configuration and carbonized. The pores of the material were then enlarged by steam treatment. And the material was given an amine functionality that improved capacity upon regeneration of the material by heating.
While the above art has provided some advantages, it has not adequately addressed the importance of adsorbent characteristics such as pore size, micropore volume, and pore size distribution. These characteristics are important because oxygen adsorption and storage on solid adsorbents is based on the interaction forces between the oxygen molecule and the surfaces on the micropores in the adsorbent.
As can be seen, there is a need for an improved adsorbent and storage system for oxygen that overcomes disadvantages of the presently known art.
In one aspect of the present invention, an oxygen cryogenic storage system adsorbent comprises a carbonized precursor material having first functional sites that adsorb and store oxygen and second functional sites that adsorb water and carbon dioxide and facilitate the release of oxygen, whereby the adsorbent is characterized by a total pore volume of between about 0.5 to 0.6 cm3/g, a median pore diameter between about 0.42 to 0.46 nm, and a BET surface area between about 1000 to 1200 m2/g.
In another aspect of the present invention, a method of making an oxygen adsorbent comprises polymerizing a monomer to produce a precursor material; carbonizing the precursor material to produce a carbonized precursor material; having functional sites that have a high capacity for oxygen and independently adsorbs carbon dioxide, water; and other trace contaminants, whereby the adsorbent is characterized by a oxygen adsorption capacity of about 50 to 70 weight/weight/%, at a pressure of about 10 mmHg, and a temperature of about xe2x88x92186xc2x0 C. as well as carbon dioxide adsorption capacity between about 30 to 40 weight/weight/%, at a pressure of about 4 mmHg and a temperature of about xe2x88x9280xc2x0 C., and water adsorption capacity between about 10 to 20 weight/weight/% at a pressure of 25 mmHg and a temperature of about 25xc2x0 C.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.